Asphalt and other like bituminous substances, whether of natural or synthetic origin (i.e., petroleum residue, coal tar residue, etc.), are widely used for applications such as roofing, waterproofing, and in particular, for paving applications where the asphalt is mixed with a variety of aggregates. During application of asphaltic substances, the same characteristics (e.g. tack), which give to asphalt its desirable application properties, also create significant problems with respect to release of these substances from truck beds, paving machines, shovels and other tools, and pressure rollers. These problems have been exacerbated recently by asphalt compositions containing polymeric modifiers which yet further increase adherence of hot asphalt to metal surfaces.
In the past, petroleum oils such as diesel fuel have been applied to truck beds, shovels, and the like to facilitate asphalt release. However, diesel fuel, when used for such applications, is now viewed as environmentally suspect. Moreover, the release effected by diesel fuel decreases over time, i.e. during lengthy trips from the asphalt source to the paving project, and incorporates the diesel fuel into the asphalt, where it can cause local soft spots, particularly upon later migration to the surface of the pavement under the influence of heat and light. Thus, diesel fuels are no longer recommended for use as asphalt release coatings.
U.S. Pat. No. 4,078,104 discloses asphalt release coatings which employ polydialkylsiloxanes such as polydimethylsiloxane, and which additionally contain from 0.1 to 90 percent by weight of aminofunctional silanes or siloxanes. The compositions may be applied neat by special spray apparatus, or dissolved in organic solvent such as naphtha. These compositions provide excellent release properties, but are expensive. Neat application requires special spray equipment, while application from solvent-containing solutions is now environmentally unacceptable.
U.S. Pat. No. 5,494,502 employs emulsions of a fatty oil derived from animal or vegetable sources, such as soybean oil, tung oil, linseed oil, olive oil, and the like, along with a surfactant which allows the oil to be dispersed in water. A crosslinked copolymer is an optional ingredient. However, the preferred method of application is by foaming with a special foaming apparatus, which severely limits ease of application. Moreover, the release characteristics are quite limited. Once water has evaporated from the formulation, the fatty oils soften the bitumen, causing the asphalt to adhere aggressively to truck beds after one initial release.
A further requirement for commercially acceptable asphalt release compositions is that they are suitable for use shortly after application. This is particularly true of aqueous emulsions due to the much slower evaporation of water as compared to volatile organic solvents, which are, in general, no longer used. Compositions which provide effective release only after extended drying periods are not suitable for use as asphalt release compositions.
It would be advantageous to provide a means of treating surfaces with asphalt release compositions which are environmentally acceptable, which can be applied without the use of organic solvents and without specialized equipment, and which provide for multiple releases from the substrate.